There certainly are parents who chose not to have a relationship with their adult children. But I think the stories that are told are not always the whole story. And I think the pain that adults feel about a child is not quite the same as the pain that children grow up with as a result of parents who are dysfunctional.
My mum's partner has no relationship with his adult children. He has made little effort over the years and any effort made has been solidly refused. The story was that he tried for many years and was such a good dad, but finally gave up when he realised they were never going to have anything to do with him. It kind of looks like he went NC with them. In reality, they went NC with him, but it sort of looks like he tried really hard to foster a relationship, but then walked away when he didn't feel he could do more. The truth is that he sexually abused at least one (possibly both) of them, was convicted, and their mum rightly protected them and did not facilitate a relationship with him.
To the outside world, it all looks very trivial, like they had a little spat and his daughters are brats and he tried, but for his own mental health, gave up after trying so hard and wanting to be such a 'good dad'. Absolutely no one knows the real story except for them (and me). It's a sad tale they tell all their friends and everyone thinks his daughters are awful selfish people who have denied him being able to know his grandchildren. I'm sure they tell the same story about me too (I am also NC with them, because of the abuse and the risk they put my children at until I found out about his history of and ongoing sexual abuse of children - he has continued to offend and my mum turns a blind eye).
Life is often much more complex than what it looks like on the outside to people who don't really know. But for most people, it's hard to tell these stories about how messed up your family is. So you get the whitewashed version, but the truth is much more complicated.
Fwiw, I never in a million years thought something like this would happen in my family. I never thought I'd be NC with my mum. I never thought she'd be an apologist for child sexual abuse. We had a great, happy normal family life growing up and she was a very involved grandparent. Until suddenly, she was angry and defensive and wanted nothing to do with us if I wasn't okay with her partner. I think until you've been there, it's very hard to imagine it could so easily be you.